The European Commission’sscience and knowledge serviceJoint Research Centre

Group Discussion I: Outstanding Research Challenges

• IAEA Technical Meeting on Structural Materials for Heavy Liquid Metal Cooled Fast Reactors, Vienna, Austria, 15-17 October 2019

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Joint Programme on Nuclear Materials (JPNM) of the European Energy Research Alliance (EERA) is coordinating sustainable nuclear materials research for a low-carbon Europe

Strategic Research Agenda (SRA) entitled Materials for Sustainable Nuclear Energy published in 2019

Available at: https://www.eera-set.eu/wp-content/uploads/Materials-for-Sustainable-Nuclear-Energy-SRA-of-the-EERA-JPNM-web-Identif.pdf

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EERA JPNM: Research Approach and Strategy Pillars

• Grand Challenge 1: Elaboration of design correlations,assessment and test procedures for the structural andfuel materials that have been selected for thedemonstrators, under the service conditions expected.This involves deployment of infrastructures for exposure toageing environments, testing of materials and production ofdata and knowledge.

• Grand Challenge 2: Development of physical modelscoupled to advanced microstructural characterizationto achieve high-level understanding and predictivecapability. These are essential assets, given the scarcity ofexperimental data and the difficulty and cost of obtainingthem.

• Grand Challenge 3: Development of innovativestructural and fuel material solutions and fabricationprocesses, in partnership with industry, to achieve superiorthermo-mechanical properties, better compatibility withcoolants and improved radiation-resistance, so as to increasesafety and improve efficiency and economy.

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PHASES à SYSTEMS↓

ESNII demonstrator FOAK (prototype)

Commercial deployment

As licensed (phase I) Evolving (phase II)

ADS (MYRRHA) Periodically

Replaced Components

Cladding: 1.4970; structures: 316L(N)

Coated 15-15Ti (FeAl, FeCrSi, FeTa, MAX phases, …) or AFA

N/A

Permanent Structural Components

316L(N)

LFR (ALFRED) Periodically

Replaced Components

Cladding and structures: (Al2O3 coated) 15-15Ti (AIM1)

Cladding and structures: Al2O3 Coated 15-15Ti or AFA

Cladding: AFA or FeCrAl ODS Structures: AFA

AFA or FeCrAl ODS, or (coated) Mo-ODS, or SiCf/SIC

Permanent Structural Components

316L(N) AFA or ferritic steel lined with AFA

EERA JPNM: Main structural materials expected to be used in the different ESNII Gen-IV systems (SFR, LFR, GFR, MYRRHA)

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Main issue Breakdown in sub-issues Materials concerned Techniques/Methods

High temperature behaviour and degradation of metals

Creep, relaxation and cyclic deformation

Austenitic steels (316L), F/M steels (Grade91)

Experiments: For long-term operation: Mechanical tests of in-service material, long-term tests, accelerated tests. Basic tests for model calibration: creep, low-cycle fatigue, crack propagation tests. Special emphasis on long hold times. Microstructural analysis to link mechanism-based models to experiments are needed. Models: For creep, relaxation and cyclic deformation, emphasis on unified visco-plastic continuum models, mechanistic models for different creep mechanism and damage crack propagation fracture mechanics Models need to be translated into Design Rules or Assessment Procedures.

Creep and creep-fatigue damage and crack propagation

Thermal ageing

Environmental compatibility between coolant and structural materials

Liquid Metal Corrosion and erosion (LMC)

Austenitic steels:316L, 15-15Ti and 15-15Ti with alumina surface protection

Mechanical tests: slow-strain rate tensile; fracture, fatigue, and creep-fatigue in flowing and stagnant conditions; Corrosion tests: Erosion and corrosion (oxidation and solution tests) in flowing conditions Qualification tests (mechanical and corrosion) for 316SS and welded components. Accelerated tests to map bounding conditions. Emphasis on long-term tests; A very careful documented control and monitoring of the test conditions (in particular oxygen control) is required for all tests. Tests to be complemented by detailed microstructural analysis (e.g. SEM, EBSD, XRD, TEM); Engineering related approaches need to be developed Coupling with models.

Liquid Metal Embrittlement in HLM (LME)

Weld procedures

Degradation modes and defect assessment

Compatibility with HLM

EERA JPNM: Main issues concerning pre-normative R&D-materials qualification, design rules, assessment & test procedures(1/4)

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EERA JPNM: Main issues concerning pre-normative R&D-materials qualification, design rules, assessment & test procedures(2/4)

Main issue Breakdown in sub-issues

Materials concerned Techniques/Methods

Radiation effects

Low temperature embrittlement & plastic flow localisation

Austenitic and F/M steels (irreplaceable & structural components)

Exposure to irradiation, also including coolant environment.

Standard mechanical test in hot cells of neutron irradiated materials (irradiated in test reactors or in-service exposed) and complementary ion/proton irradiation.

These tests need to be supported by irradiation models

Transfer the data into reduction factors for material properties.

Long-term/low dose irradiation in environment

High dose irradiation swelling and creep

Fuel cladding materials: 15-15-Ti austenitic steel

Assessment of complex loadings

Non-isothermal thermo-mechanical loads

All

Experiments:

Component or specimen tests that simulate thermo-mechanical loads (e.g. thermal shocks), variable amplitude tests for fatigue; tensile high strain rate tests, multi-axial tests, e.g. cruciform specimen for biaxial loading.

Modelling:

Finite element models of complex load cases and simplification to translate into design rule load cases.

Complex stress distributions

Load transients and beyond design conditions

Weld procedures

Degradation modes and defect assessment

Compatibility with HLM

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EERA JPNM: Main issues concerning pre-normative R&D -materials qualification, design rules, assessment & test procedures(3/4)

Main issue Breakdown in sub-issues

Materials concerned Techniques/Methods

Integrity and qualification of weldments and welded components

Residual stresses

All welds:

austenitic, F/M; Ni-based alloys and dissimilar metal welds

Modelling:

Simulation of weld process and post-weld heat treatment for residual stresses;

Structural integrity assessment (defect assessment crack propagation, damage) of welded specimens and components by FEM.

Translation of structural analysis assessment into Design Rules.

Weld procedures

Degradation modes and defect assessment

Compatibility with HLM

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EERA JPNM: Main issues concerning pre-normative R&D -materials qualification, design rules, assessment & test procedures(4/4)

Main issue Breakdown in sub-issues

Materials concerned Techniques/Methods

Sub-size and miniature specimen test standardization

Sub-sized/ miniaturised specimens for mechanical property

Fuel cladding material, 15-15Ti

Experiments:

Various fuel cladding tests (internal pressure, ring-compression, small-punch, cone mandrel) with emphasis on hot-cell tests;

Small-punch test for tensile and creep properties;

Nano-indentation, micro-pillar tests for tensile properties;

miniature specimen fracture and fatigue tests.

Modelling:

Test to be complemented with finite element analyses, and meso-scale models (dislocation dynamics and crystal plasticity)

Thin-walled cladding tubes

Small Punch test All

Micro-pillar tests and nano-indentation All

Component and material health monitoring

All

Patterns of response of material to NDE techniques as part of codification;

Exploration of possibility of lifetime estimation based on NDE in view of online monitoring

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EERA JPNM: Summary of issues relevant to the different structural material classes and types (1/4)

Type of related issues

Materials

Pre-normative research

Modelling Advanced materials’ solutions

Austenitic steels

316L(N)

(prototype irreplaceable components)

Thermal ageing, thermal creep, compatibility with heavy liquid metals (HLM): increased database (including welds),

accelerated testing, models describing micro/macro evolution à refinement of existing, or elaboration of new,

design rules

Improve compatibility with coolants, apply high temperature protective

barriers

15-15Ti (cladding)

Irradiation creep and swelling, thermal creep, compatibility with coolants & fuel: increased database, models describing

micro/macro evolution à refinement of existing, or elaboration of new, design rules

Improve swelling resistance and compatibility with coolants (apply high

temperature protective barriers).

Alumina forming austenitic (AFA)

steels

Exposure needed for screening between

candidates

Thermodynamic models for composition optimisation,

microstructure evolution models

Addition of Al increases compatibility with coolants (protective alumina

layer), but causes embrittlement at low T, although improves high T creep

strength (NiAl precipitates): compromise searched

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EERA JPNM: Summary of issues relevant to the different structural material classes and types (2/4)

Type of related issues

Materials

Pre-normative research Modelling Advanced materials’ solutions

Ferritic / Martensitic (F/M) steels (cladding and core)

9-14 %Cr

Low temperature irradiation embrittlement, irradiation creep, thermal ageing/creep, creep-fatigue (cyclic operation

softening) compatibility with coolants, liquid metal embrittlement: increase database (including welds), models

à define design rules and develop models in support

Need solution to minimize embrittlement, improve creep

resistance (e.g. by thermomechanical treatment) and improve compatibility with

coolants

Oxide dispersion

strengthened (ODS)

Exposure needed for screening between candidates, suitable treatments for recrystallization to eliminate anisotropy after

powder metallurgy production of bars and tubes by extrusion.

Oxide formation/stability, microstructure evolution,

modes of deformation

ODS steels (tubes) have better creep resistance, but

manufacturing and joining are issues (optimization needed);

toughness and compatibility are also issues

FeCrAl alloys (also ODS)

Thermodynamic models for composition

optimisation, microstructure evolution

models

Addition of Al increases compatibility with coolants

(protective alumina layer), but worsens mechanical behaviour:

compromise searched

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EERA JPNM: Summary of issues relevant to the different structural material classes and types (3/4)

Type of related issues

Materials

Pre-normative research Modelling Advanced materials’ solutions

Refractory metallic alloys (cladding and core)

Molybdenum alloys (including

ODS)

Exposure needed for screening between candidates. Irradiation creep and swelling, thermal creep, compatibility with coolants & fuel: increase database, models describing

micro/macro evolution à refinement of existing, or elaboration of new, design rules, supported by models

Prospective materials, mainly for cladding, studied also in the past, with problems of manufacturing, compatibility with coolant and

mechanical behaviour Vanadium

alloys

High Entropy Alloys

Prospective metallic materials with potentially excellent mechanical properties, coolant & radiation resistance, need extensive investigation for screening, including understanding of

origin of properties through modelling, before applications are identified.

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EERA JPNM: Summary of issues relevant to the different structural material classes and types (4/4)

Type of related issues

Materials

Pre-normative research Modelling Advanced materials’ solutions

Ceramics (cladding and coating)

SiC/SiC (also C/C) composites

(cladding)

Mechanical test standardization, radiation resistance (thermal

conductivity, hermeticity, swelling, …) and corrosion resistance à

define design rules

Microstructure evolution models under irradiation, finite element models for

composite architectures, X-ray tomography techniques

Liners to guarantee hermeticity of cladding, or

other techniques to guarantee hermeticity. Limit thermal conductivity degradation

under irradiation.

Non-metallic core support structures (ad hoc ceramics)

Screening of candidates. Test standardization (mechanical &

thermophysical properties)

Microstructure evolution models under irradiation

Protection against oxidation

Al2O3 coatings Applied with different techniques on different substrates to protect against coolant attack and

temperature: exposure for screening and qualification

Max phases

Prospective ceramic materials with excellent mechanical properties (for ceramics), coolant and radiation resistant, though stability to high temperature needs to be verified case by case. Need

extensive investigation for screening, including understanding of origin of properties, before applications are identified. Usable as coatings.

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• Discuss and identify R&D needs and gaps to assess the future requirements in the field, which should eventually lead to efforts being concentrated in the key lacking areas

• Enable the integration of research on materials in Member States (e.g. development of materials for operating in corrosive/severe environments, study of physics and chemistry of the process, design of dedicated experimental facilities and development of computational tools for material characterizations etc.) to support the development of new technologies that have a higher level oftechnological readiness

• Provide recommendations to the IAEA for future joint efforts and coordinated research activities (if required) in the field

Objectives of the Technical Meeting

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Possible discussion topics

• Discuss update / complementation of R&D needs

• Attempt prioritization of R&D needs to support deployment of HLM-cooled reactors

• Provide possible recommendations to IAEA for possible future joint efforts

o Proposal of the GIF LFR System Steering Committee (SSC) discussed at the meeting on 8-10 Oct 2019 to establish an expert team (group) to develop start-of-the-art evaluations of available corrosion resistance data of candidate structural materials for HLM-cooled concepts

o Provide authoritative recommendations to designers and safety authorities in support to licensing

o Format: to be discussed (should be peer-reviewed)